The present invention relates to an engine starter motor system and more particularly to a belt driven engine starter for an internal combustion engine.
Internal combustion engines are typically started by a dedicated electric starter motor mounted to the engine. In the typical configuration, the starter motor receives a signal from the vehicle operator to start the engine. A gear mounted to a pinion in the electric starter motor advances from the electric starter and meshes with a ring gear attached to the crankshaft of the engine. Once the ring gear and the electric motor gear have meshed, the electric starter motor rotates, thus turning the ring gear attached to the crankshaft. Turning of the ring gear consequently turns the engine and with the engine ignition system energized the engine starts.
Electric starter motors that drive the ring gear of the engine are typically geared in a range from about ten-to-one up to fifteen-to-one. Setting the arithmetic ratio between the starter motor gear teeth and the ring gear teeth attached to the crankshaft to about ten-to-one up to fifteen-to-one accomplishes this. As such, typical electric starter motor systems take generally one second to achieve engine crankshaft rotational speeds of one hundred twenty-five revolutions per minute under warm engine conditions. While a warmer engine may start quicker than a cold engine, a typical electric engine starter that is meshed to a ring gear due to the fixed gear ratio will generally take at least the aforementioned one second to produce an engine speed sufficient to start an internal combustion engine at any anticipated ambient temperature.
Whether or not an engine will start faster, the performance of the engine starter motor is generally the same, even though the performance required from an electric starter motor to start a warm engine is less than what is required to start a cold engine. For example, the electric motor turns the engine between fifty to one hundred twenty-five revolutions per minute and the starting sequence still takes at least one second whether the engine is cold or warm. It is, therefore, desirable to take advantage of the ability to start a warm engine at faster engine speeds and shorter engine starting durations.
It is also desirable to have an electric engine starter that is not otherwise limited to the gear ratio range from ten to one up to fifteen to one as to more easily increase the engine speeds during engine start. It also desirable to have an electric starter motor that is faster, so that faster engine speeds are achievable during the startup sequence and the time required to achieve the faster engine speeds is shorter.
Other typical electric starter motors that are configured with ring gears attempt to achieve faster engine speeds during the start sequence to produce faster engine starting times. These faster systems, however, employ forty-two volt electrical systems over the prevalent and less expensive twelve volt systems. While the forty-two volt system may achieve desired engine starting performance, implementation of a forty-two volt system remains a costly endeavor. Implementing a forty-two volt system solely for the electric starter motor system requires the added complexity of multiple systems running with different voltages in the vehicle. Implementing a vehicle-wide forty-two volt system would result in redesigning and retooling multiple electrical sub-systems in the vehicle just to satisfy the demand for only a forty-two volt engine starter system. It is, therefore, desirable to use a twelve volt electric starter motor as to avoid the costs associated with a forty-two volt alternative.
Shutting down the engine when there is no demand for engine power and restarting the engine when a demand is present is a common scheme to reduce fuel consumption when using an internal combustion engine. It has not, however, been advantageous to do so on a vehicle that only has one power source. For example, a driver in a typical vehicle with an internal combustion engine would face an excessive delay waiting for the engine to restart with a typical electric starter motor meshed to a ring gear. The excessive delay is due to the above mentioned time required to start the engine due to inability to turn the engine faster. It is, therefore, desirable to restart a warm engine without excessive delays so that an engine can be restarted in a single power source vehicle to reduce fuel consumption.
Shutting down the internal combustion engine when there is no demand for engine power and restarting the engine when a demand is present is a common scheme to reduce fuel consumption in a hybrid vehicle when using an electric and internal combustion engine. While methods to restart the internal combustion engine on a hybrid vehicle are common, an electric motor meshed to a ring gear remains the typical simple arrangement to start the engine. While this arrangement suffers from the drawbacks mentioned above for a non-hybrid vehicle, it also has the additional drawback of the typical electric starter motor drawing more energy then is otherwise needed to start a warm engine. The need to conserve energy is inherent to the design paradigm of a hybrid vehicle. As such, it is, therefore, desirable to have an electric starter for a hybrid engine that starts the internal combustion engine faster and uses less energy.
The present invention is directed to a belt driven starter motor system used, for example, to start an internal combustion engine. The system comprises a starter motor including a rotor and a pulley, a crankshaft pulley, and a belt tensioner, which are connected by a drive belt. The belt tensioner has a movable first pulley and a movable second pulley. At rest, both pulleys apply tension to the drive belt. The starter motor rotor begins rotation prior to the initial rotation of the crankshaft pulley where the first pulley withdraws and the second pulley advances to maintain belt tension. This allows the starter motor rotor to use rotational energy to initiate rotation of the crankshaft pulley and the crankshaft. This facilitates the rapid start of the internal combustion engine.
In another aspect, the present invention is directed to a belt driven starter motor system where a belt tensioner device is absent. The system includes a crankshaft and a pulley and a starter motor having a rotor and a pulley, which are connected by a drive belt. The system also comprises a delay device for delaying rotation of the crankshaft pulley for a predetermined time period or rotational displacement of the starter motor rotor after initiation of the starter motor rotor rotation. This allows build-up of rotational energy in the rotor for use in subsequent rotation of the crankshaft pulley to start the internal combustion engine. Thus, the starter motor rotor begins rotation prior to rotation of the crankshaft pulley, wherein the rotor partially uses rotational energy to rotate the crankshaft pulley to start the internal combustion engine.
The starter motor rotor uses the rotational energy stored as it rotates prior to the time in which the crankshaft pulley begins to rotate. The delay in rotation is achievable by providing slack in the belt that connects the starter motor to the crankshaft pulley, such that the starter motor pulley, attached to the starter motor rotor, rotates to take up the slack on the belt. Once the starter motor has rotated to the point where there is no longer slack in the belt but now tension, the crankshaft pulley begins to move due to the rotational force exerted by the starter motor pulley. The starter motor, however, has begun to rotate before the crankshaft pulley. As such, the electrical energy needed to generate the rotational force to turn the crankshaft pulley is less than what would be needed if the starter motor began to rotate at same time as the crankshaft pulley, due to the fact the starter motor rotor has stored rotational energy.
In one embodiment of the invention, a bi-directional belt tensioner is used to control tension on the belt. The bi-directional belt tensioner has two pulleys, which are interconnected by a spring. As the starter motor rotor begins to rotate, the first pulley begins to back off the belt as the starter motor pulley exerts a force on the belt creating tension. The rotational force generated by the starter motor creates enough tension in the belt to move the first pulley, but not enough to initiate rotation of the crankshaft pulley. Movement of the first pulley consequently provides slack in the belt. Contemporaneously, the starter motor pulley rotates to remove slack in the belt, which ultimately results in maintenance of tension in the belt. The motion of the belt tensioner pulley in concert with rotation of the starter motor pulley allows the starter motor rotor to begin rotation prior to the rotation of the crankshaft pulley.
In another embodiment of the invention the bi-directional tensioner is absent and a delay device is used integral to the starter motor, so that the starter motor rotor is able to spin up before the starter motor pulley engages the belt to subsequently rotate the crankshaft pulley. One such device is a torsion spring integral to the starter motor pulley, whereby the starter motor begins to rotate and apply tension to the spring. Only after enough tension is created in the spring, will the starter motor pulley begin to rotate. As such, the rotor begins to rotate prior to the crankshaft pulley, thus storing rotational energy which is then used to assist in starting the engine. One other such delay device includes a clutch within the starter motor such that rotational speed of the rotor increases to a point in time where the clutch would engage thereby causing the starter motor pulley to engage the belt. At that point the crankshaft pulley would begin to rotate, such that the starter motor rotor would begin to rotate prior to the crankshaft pulley, thus storing rotational energy which is then used to assist in starting the engine. One other such delay device includes a threaded rotor integral to the starter motor. The starter motor rotates such that the threaded rotor spins within the starter motor pulley such that the rotor spins freely as the threads advance within the pulley. Ultimately, the pulley will encounter a stop at the end of the threads, and at that time the pulley begins to rotate with the starter motor. As such, the starter motor rotor is able to rotate prior to the crankshaft pulley, thus storing rotational energy which is then used to assist in starting the engine.
The devices illustrated above are not exhaustive and as such are not intended to limit the scope of the disclosure in any manner. Those skilled in the art will readily appreciate alternative ways to delay rotation of the starter motor rotor prior to engaging the starter motor pulley.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.